1. Field of the Invention
The present invention relates to a temperature sensor circuit.
2. Description of the Related Art
A conventional temperature sensor circuit will be described. FIG. 6 is a schematic diagram showing the conventional temperature sensor circuit.
The temperature sensor circuit includes a constant current circuit 11 and a Darlington circuit. The constant current circuit 11 includes a constant current source 21 and a current mirror circuit composed of MOS transistors 41 and 44 having the same size. The Darlington circuit includes bipolar transistors 61 to 63 having the same size. An output terminal of the constant current circuit 11 is connected with an emitter of the bipolar transistor 63 of the Darlington circuit.
According to the temperature sensor circuit, base-emitter voltages of the bipolar transistors 61 to 63 vary with a temperature and an output voltage of the temperature sensor circuit also varies correspondingly. The temperature is detected based on the output voltage (see, for example, JP 05-248962 A).
However, there are manufacturing variations in current gains of the plurality of bipolar transistors of the Darlington circuit, so emitter currents vary. Therefore, the base-emitter voltages of the bipolar transistors vary, so the output voltage of the temperature sensor circuit varies to reduce the precision thereof.